One possible explanation is that the economy’s good health masks continued hard times for men and women in their 20s and early 30s, who are responsible for most baby-making. “This young generation, millennials, I think they still feel pretty uncertain, as if they can’t afford to make this big long-term commitment” to raising a family, says Karen Guzzo, a sociologist at Bowling Green State University. “They have these standards: ‘I want to live in a good neighborhood. I want to have a house. I want to be able to have good child care and take time off from working.’ ”

The 3.9 percent unemployment rate in April seems to indicate that jobs shouldn’t be a problem for people considering parenthood. But the share of twentysomething men who are employed still hasn’t fully recovered from the blow of the recession. As of April it was down 2.4 percentage points for men age 20-24 (to 68.4 percent) and 2.2 percentage points for men age 25-29 (to 83.7 percent) compared with the last business cycle peak, December 2007, according to the Bureau of Labor Statistics. Some of those young men who aren’t employed are in school; some would take a job but aren’t actively searching. In any case, the drop in the employment-to-population ratio is an important number because “in the fertility literature, the No. 1 determinant is the husband’s employment status,” says Steven Lugauer, an economist in the University of Kentucky’s Gatton College of Business and Economics.